1. Field of the Invention
The present invention relates to a method and apparatus for measuring the wheel alignment of a vehicle.
2. Description of the Related Art
In a vehicle, a wheel is provided with a camber angle to secure steerage during driving and the wheel is provided with a toe angle to prevent a decrease in straight-running stability caused by the provision of the camber angle. Further, in order to fix the wheel alignment so as to achieve good driving stability, it is necessary to measure the angle and position of each wheel with high accuracy. Wheel alignment measurement is generally performed for a finished vehicle with wheels mounted thereon. In this case, however, for example, the wheel alignment measurement is performed based on the position and attitude of the side wall of each wheel (tire and road wheel). This could lead to an error in the measurement result according to elastic deformation of the tire, a road wheel mounting state, and the like, and the measurement result is useless in fixing the wheel alignment with accuracy.
On the other hand, conventionally, the vehicle alignment is measured via wheel mounting portions without the wheels mounted in an assembly line for assembling a vehicle body in order to improve the productivity of the vehicle. More specifically, in the vehicle body assembly line, steering gears and suspensions are installed and thereafter a load equivalent to the vehicle weight is applied to the wheel mounting portions in a state where the wheel mounting portions without the wheels mounted thereon are elevated relatively to the vehicle body, and then the position and attitude of the wheel mounting portions are detected to measure the wheel alignment. Thereby, the position and attitude of the wheel mounting portions are detected without the wheels, and therefore it is possible to obtain a measurement result unaffected by the elastic deformation and mounting state of the wheels.
Since, however, the wheel alignment measurement performed for the wheel mounting portions on which wheels are not mounted differs in the ground contact state or load-applied state from a measurement for the wheel mounting portions on which the wheels are mounted, it is insufficient to obtain high measurement accuracy.